Method and apparatus for the production of magnesium



May 23, 1944. H. P. DAVIS 2,349,409

METHOD AND APPARATUS FOR PRODUCTION OF MAGNESIUM Original Filed Feb.20,' 1942 2 Sheets-Sheet 1 H. P. DAVIS May 23, 1944.

METHOD AND APPARATUS FOR THE PRODUCTION OF MAGNESIUM Original Filed Feb.20, 1942 2 Sheets-Sheet 2 INVENTOR. HARRY P DAW 5, eased,

Dec C1A/217A DAV/s,

Patented Mayl239 1944 METHOD AND APPARATUS FOR' PRO- DUCTION 0FMAGNESIUIK Harry P. Davis. deceased, late ofvPalo Alto, Calif., byClarita Davis, administratrix, Palo Alto, Calif., assigner, by mesneassignments, to The Anglo California National Bank of San Francisco, SanFrancisco, Califga national banking association, as trustee for 'thebenefit of Reconstruction Finance Corporation, San Francisco, Calif., acorporation of the United States Original application February 20, 1942,Serial No. 431.752. Divided and this application April 29. )1943, SerialNo. 485,000

i Claims. (Cl. 266-10) This application is a division ofthe'aapplication Serial No. 431,752, for Methods rand appa ratus for theproduction of magnesium, iiled by Harry P. Davis on February 20, 1942.

This invention relates to. the production of metallic magnesium by thereduction of magnesium oxide-containing raw material, particularly ofburned dolomite or magnesite, with the aid of a reducing agent such assilicon (ferrosilicon), or aluminum or a mixture of both. or of similarreducing agents which donot generate gaseous products of oxidation. Y

It is well known that in eecting the above reduction operation with theuse of a continuously fed furnace. various diiliculties are encountered,as well inthe type in which the operation is effected at a temperatureabove the melting point of the reaction components, as in the other typein which the mixture is heated at a temperature below its melting point.Both processes are disadvantageous. The reduction of magnesia in theliquid state is a .rather slow reaction, leaving behind a considerableproportion of the unaltered magnesia; moreover disengagement of themagnesium vapor from the molten metal mass is dif cult; nally there isan appreciable attack on the furnace lining by the -molten slag. On thevother hand reduction exclusively in the solid `state,. while proceedingat a more rapid rate, givesv rise to dimculties in removing the spentresidue; moreover, serious difculties arise from the fact that inconducting the operation such a's to obtain economical rates 4of vaporilow, the

g vapor evolved willcarry over dusty impurities into the condenser, as aconsequenceoi' which there willnot be recovered metal answering as topractical purity requirements.

The art has therefore resorted to intermittent processes. But operationsof this kind have generally the disadvantage of being tedious. `'I'hisis in particular the case with magnesium reduction since it is necessaryto wait before discharging the retort, unta 1t cools to a temperaturen;-

low Bil-100 C., since otherwise'the magnesium would react with theatmospheric oxygen and"r nitrogen, which reaction may beso violent thatthe magnesium' may beset on fire.

litl is the object of thev invention to reduce the' k time required forcarrying out the whole cycle of operation to a minimum, and tov enablethereby the operation vto ne carried out on a very large scale withoutthe use ofan excessive amount 'of retort units; A.Another object of theinvention is to facilitate the removal of the spent residue .fromv' thezone of the reaction. -A further object o! the'invention is to 'enablethe magnesium vapor to-be disengaged at a rate highl enough i Figure 2is a section taken on the line A-A' of Figure l;

Figure 3 is a fragmentary section taken on an enlarged scale,showing'details of the apparatus;

Figure 4 is a horizontal section showing an alternative embodiment .ofthe apparatus;

Figure 5 is a'view of details in connection with the briquettes to befed into the apparatus'.

Referring. first to Figure l, a relatively long steel cylinder I whichhas a closed bottom. and -is equipped with a releasable cover 2 at thehead, and a discharging device 3 with a door I at the bottom, forms theouter shell of the apparatus." This. outer shell is insulated by arefractory lining 5 impermeable for gases. In the interior of thevertical shaft 24 enclosed, which constitutes' Inside the retort thereis centrally displaced a e tubular electric resistance heating device 9,resting by supports i0,` on the inwardly inclined wall of the dischargedevicel 3. A larger annular electric heating device H, is disposed onvthe inside of the refractory lining 5. Within the annular interspacebetween the outer and the inner cen-r 'trai heating device. there areplaced' a. plurality. for instance 8, Vof tubular members-i2. destinedfor receiving the charge I3. which are provided with means I4 adapted toform a substantially unobstructed passageway `for the vapor releasedfrom the charge, and centrally disposed within the charge so as toreduce, by displacement, the

radial extent thereof. In the' case as shown in' the drawingsfthesaidcentral duct member com` prises a tube Il having round about a largenumber of perorations from end t end, therebypermitting the charge I3which occupies the annular space between said duct member. and theinside wall ofthe tube, to be uniformly supplied with heat, and thusalso to disengage magnesium va por uniformly throughout the entirereacting mass. tightly tting plate I5, Welded or otherwise se- Theinterior of the retort is covered by a cured to the open upper end oi'the central h`eating device 9, and the charge container tubes I2 passedthrough round about the said heating device, a vent pipe I6 connectingthe interior of A device 9 to the evacuating means being providedthereupon and all of the joints being sealed by a sand seal I'I heapedupon the plate I5. At their open under ends the tubular heating device 9and the charge container tubes I2 are -sealed by another bottom sandlseal I 8. 'I'he object of both these seals is substantially to preventthe metallic vapor evolved from entering into interspaces where theyarenot wanted, and thus coming into contact with the heating elements andbrick' work. At the upper ends the charge container tubes I 2, areprovided with a conical cap or cover I9 which islperforated to form ascreen. After the removal of the cover 2 and lifting out the condenser6, the charge is fed in, and is spread by the cones I9 in the openannular space between the duct member I4 and the inside Wall of thetubes I2, up to a level somewhat below the plate I5. Thereuponcondenser' 6 is dropped -down into position, cover 2 closed and vacuumapplied throughthe connection 8 to produce residual pressure below -twomillimeters. Heat is now applied by means of theheating elements 9 andII' to maintain the charge at a temperature causing active vaporizationbelow the melting point of magnesium. The vapor disengagedesspace 20,between an outer ring 2| and an inner ring 22, which interspace isintended to receive the charge. The duct members I4 are disposed, atregular intervals, in the vcharge itself.' The operation ,of this formof'the device is apparent from the foregoing description.

For eiecting reduction with the aid of ferrosilicon, for instance 100parts by weight of burned dolomite, may be mixed up with 13.8 parts4 byweight of ferrosilicon. With a vacuum of about 0.1 millimeter reductiontakes place at about 1150 C.

What is claimed is:

l. An apparatus for the production of metallic magnesiumby reducingmagnesium oxide-containing material with the aid of reducing agentscapable of exclusively 'furnishing solid reduction products, comprisingin combination a longitudinally extended receptacle of substantiallytubu-l lar shape, closed at the bottom of the lower portion adapted tobe heated to serve as a retort and provided with a removable cover atthe top of the upper portion adapted to'be kept cool to serve as acondenser, and a plurality of vapor-conducting means uniformly beingembedded in the 'surrounding charge and adapted to establish propercommunicationV between the interior of the I charge and the commoncondenser.

capes-through the lateral openings of the central duct members I4, ofthe charge container tubes e I2, and rises-in the condenser 6, where itcondenses as a thick annular deposit of crystalline character, adheringto the inner surface. 'I'here follow the steps of completely coolingdown,

sweeping out by a gas indifferent to magnesium f *(.which is introducedand withdrawn by suitably positioned pipes not shown in the drawings),A.opening cover 2, and lifting out the condenser 6 for recovering thesublimate. The bottom cover 4 can now be opened to discharge the bottomsand seal, and thereupon also the spent residues by gravity. llnallythebottom opening is closed l by cover 4, and the bottom sand sealrearranged agent underl treatment. After reintroducing the briquets, forinstance of (Figure 5) ovoid shape, 1-

whichare preferably preheated in the compactedstate, to a temperature of70D-900 C., to free them substantially completely from carbon dioxide,and to save time and'energy in the 'operation of the electric retortfurnace. ,e u Materials preferablyuused for arranging the sand seals aremagnesium oxide, or spent residues of the operation, both in very finesubdivision.

In Figure -4 .there is another embodiment of the invention described, inwhich the charge con- 2. An apparatus for the production of metallicvmagnesium by reducing magnesium oxide-containing material with the aidof reducing agents capable of ,exclusively furnishing solid reductionproducts, comprising in combination a longitudinally'extended receptacleof substantially tubular shape, closedat the bottomof the lower portionadaptedto be heated to serve as a retort and provided with a removablecover at the top of the upper portion adapted to be kept cool to serveas a condenser. a removable condenser liner positioned in the upperportion, sealing means for preventing the passage of vapor from theheated portion to enter into 'the interspace between the condenser linerand the receptacle wall, a plur rality of vapor-conducting means beinguniformly embedded in the surrounding charge and capable of causing thevapor to escape through a plurality of relatively small passageways intothe .common condenser.

3. An apparatus for the production of metallic magnesium by reducingmagnesium oxide-containing material With the aid of reducing agentscapable of exclusively furnishing solid reduction products, comprisingin combination a longitudinally extended receptacle of substantiallytubular shape, closed at the bottom of the lower portion adapted to beheated to serve as a retort and provided with a removable cover at thetop of the Y upper portion adapted to be kept cool to serve as acondenser, a removable condenser liner of the split type positioned inthe upper portion, sealing means for preventing the passage of vaporfrom the heated portion to enter into the interspace between thecondenser liner and the receptacle wall.' a plurality ofvapor-conducting means uniformly being embedded in the surroundingcharge and capable of causing the vapor to escape through a plurality ofrelatively smallv passageways Ainto the common condenser.

'Adminstratrx of. the Estate tainer tubes I2 are replaced by 'an annularinter- 75 v 4. Inan apparatus as defined in claim 1 a bottom sand sealand means for discharging the sealing material, and thereby alsodischargingV .the spent residue by gravity.

A CLARITA DAVIS,

of Harry P. Davis,

